Facilitator/Educator Guide: Plop, Plop, Fizz Fast: The Effect of Temperature on Reaction Time

Have you ever seen bubbles form when an Alka-Seltzer tablet is dropped into water? Have you wondered how the water's temperature affects how quickly those bubbles form? Find out using Alka-Seltzer tablets, jars or drinking glasses, ice cubes, and a stopwatch or timer.

Background Information

Alka-Seltzer® is a medical drug that works as a pain reliever and an antacid (antacids help neutralize stomach acidity — e.g., heartburn). The pain reliever used is aspirin and the antacid used is baking soda (sodium bicarbonate, NaHCO3).

To take the tablets, you should fully dissolve them in a glass of water, where they famously undergo a chemical reaction that produces lots of carbon dioxide (CO2) bubbles. As the tablets dissolve, the sodium bicarbonate splits apart to form bicarbonate (HCO3-). This reacts with hydrogen (H+) from citric acid, another ingredient in the tablets. This chemical reaction forms water and carbon dioxide gas.

[Please enable JavaScript to view equation]Equation 1. When Alka-Seltzer tablets are dissolved in water, bicarbonate forms (from the sodium bicarbonate), which in turn reacts with hydrogen (from citric acid) to form water and carbon dioxide gas.

For the reaction to occur, however, the bicarbonate must come into contact with the hydrogen in just the right way. The probability of the bicarbonate and hydrogen doing this is affected by temperature: the higher the temperature, the faster the molecules move; the lower the temperature, the slower they move.

In this science activity, students will use Alka-Seltzer tablets, water at two different temperatures, and a stopwatch to investigate how temperature affects the speed of the bicarbonate reaction.

For Discussion

This science activity can serve as a starting point for a variety of science and health discussions. Here are a few examples of questions that can be used to start a discussion:

What ingredients make Alka-Seltzer work as a pain reliever and an antacid?

How do you think hot water will change the speed of the bicarbonate reaction compared to cold water?

How do antacids work?

What other factors beside temperature can affect how well a chemical reaction takes place?

What other reactions can you think of that temperature affects?

Materials

Needed for preparing ahead:

Clear jars (2 for each demo or small group). They should be identical. Clear drinking glasses, plastic cups, bottles, or vases can also be substituted.

Ice cubes (enough to fill one of the jars or other receptacles you are using halfway for each demo or small group)

Cold tap water (enough to fill one of the jars nearly full for each demo or small group)

Spoon (1)

Hot tap water (enough to fill a jar nearly full for each demo or small group)

Optional: Thermos bottle (1)

Alternative Version: For a more colorful and engaging activity turn each reaction into a home-made lava lamp. The rate of the Alka-Seltzer's effervescence will dictate the rate of colored bubbles ascending the lava lamp. To do this version, you will also need to include the following materials:

Vegetable oil (enough to fill two bottles/jars nearly full for each demo or small group)

Food coloring (10 drops)

A way to make one bottle/jar hot and one cold, such as by using a large bowl with hot water (enough to fill the bowl) and a refrigerator or freezer (1)

Knife (1)

Cutting board (1)

Alka-Seltzer tablet (1)

Note: For the most visual impact choose tall jars or empty clear plastic 1-liter or 2-liter bottles. You only need a small amount of the cold tap water and hot tap water — enough to fill each bottle/jar with 1-2 inches of water.

Needed for each demo or small group at the time of the science activity:

Alternative Version: For the lava lamp version the jars/bottles should not be filled full of water. Instead each bottle should have 1-2 inches of colored water and then be filled nearly full with vegetable oil. One bottle should be hot and one should be cold. You will also want to quarter the Alka-Seltzer tablets to avoid having them float to the top of the bottles.

Figure 1.
You need only a few simple household materials to do this fun science activity.

What to Do

Prepare Ahead (< 10 minutes)

For each demo or small group, fill one of the jars, drinking glasses, or vases halfway with ice cubes.

Figure 2.
For each group or small demo, fill a jar halfway with ice cubes.

Add cold tap water to the jar with ice cubes to about an inch from the rim. Use the spoon to stir the ice cubes in the jar for about a minute so that the temperature equilibrates.

Also for each demo or small group, add hot tap water to the second, empty jar till about an inch from the rim. If you do not begin the activity immediately after preparing it, store the hot water in a thermos bottle until you are ready.

Figure 3.
For each group or small demo, prepare one jar with ice water and a second jar with hot tap water.

Immediately before doing the activity, use the spoon to remove the ice cubes from the ice-water jar.

Alternative Version: If you want to do this activity using the lava lamp setup you will need to make a few modifications. Fill each bottle/jar with 1-2 inches of water, add 5 drops of food coloring to each bottle, and then fill the bottles at least three-quarters full with vegetable oil. To do the activity, you will need to somehow make one prepared bottle be hot and one cold. (For example, to make one hot you could let it sit in a large bowl of hot water, and to make one cold you could store it in a refrigerator or freezer.) Cut an Alka-Seltzer tablet into quarters. Only two quarter pieces are needed for the activity, but having additional pieces can be useful.

Science Activity (< 10 minutes)

Each classroom demo or small group should have two intact Alka-Seltzer tablets, one jar with ice-cold water, one jar with hot water, and a timer or clock that shows seconds.

Have students work in pairs.

Ask one student to drop a tablet in the jar with hot water while the second student times how long it takes for the tablet to disappear. There is a data table in the Student Guide that they may use to record their data. Ask students to make observations and report their data.

Figure 4.
Have one student drop an Alka-Seltzer tablet in the jar while the second student times how long it takes for the tablet to disappear.

Figure 5.
If you do the alternative version using vegetable oil and food coloring, the students' bottles should look similar to this one. Students should use one quarter of an Alka-Seltzer tablet with this setup, to prevent the tablet from floating to the top, and time how long the tablet piece takes to disappear. As the tablet piece dissolves bubbles will form, pushing the colored water up through the oil layer. The effect will look like a home-made lava lamp.

Figure 6.
Have students watch the jar until the tablet completely dissolves.

Now have one student drop a tablet in the jar with the ice cold water while the second student times how long it takes for the tablet to disappear. Again, ask students to make observations and report their data.

Alternative version: If doing the lava lamp version the groups should drop a quarter of a tablet into each vegetable oil and colored water bottle. This will prevent the tablet from floating to the top of the oil layer and ensure that students get the full lava lamp effect. Note that the tablet piece may take a moment to sink through the vegetable oil to reach the water, where it will react. Have students start timing as soon as the tablet piece reaches the water and starts reacting.

Expected Results

When the Alka-Seltzer tablet was added to the hot water, the tablet should have quickly dissolved, taking around 20 to 30 seconds to do so, depending on the exact temperature. When the tablet was added to the ice-cold water, it should have taken much longer to dissolve, with most of the tablet dissolving after about two to three minutes, but with some bubbles (from the tablet's remains) still apparent after six minutes or longer. In the hot water, the tablet should have more vigorously produced bubbles than in the cold water. The higher the temperature, the faster the molecules move, and the more likely it is that bicarbonate will contact hydrogen in just the right way for the chemical reaction to occur and produce carbon dioxide bubbles.

Alternative Version: If the home-made lava lamp setup was used the same difference in rate of reaction should have been observed. In addition, the bubbles formed in water layer during the reaction should have floated to the top, looking like colorful blobs as they moved through the oil layer and then burst at the top (releasing the carbon dioxide gas), and then the blobs of food coloring should have sunk back to the bottom (now empty of the carbon dioxide gas). The effect should have been reminiscent of a lava lamp.

For Further Exploration

This science activity can be expanded or modified in a number of ways. Here are a few options:

Test Alka-Seltzer tablets in a wider range of temperatures, and then graph the time it takes a tablet to dissolve in water at each temperature (checked with a thermometer) to better understand how temperature affects the chemical reaction. What temperature change is required to increase the reaction time by a factor of two? What about decreasing the reaction time by a factor of two?

Students could investigate how the surface area of the Alka-Seltzer tablets affects the chemical reaction by breaking the tablets into pieces. If there is a greater surface area (i.e., a tablet is broken up into more pieces), does the same amount of tablet result in the reaction happening faster or slower?

For an advanced challenge, have students repeat this activity several times to see how much variation their results have, then calculate the standard deviation. (Check the temperatures using a thermometer.) How much variation is there for the reaction time at a given temperature?

Credits

You can find this page online at: http://www.sciencebuddies.org/science-fair-projects/Classroom_Activity_Educator_Temperature_Reaction_Time.shtml?from=Blog

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